Data and signal line chokes
Selection guide
Surface-mount types
Design
Double chokes
B82788C0/S0
42
0.011 … 150 …
0.1
300
0.011 … 150 …
0.1
300
I core, EIA size 1210,
for automotive, industrial
and telecom applications
I core, EIA size 1812,
for automotive, industrial
and telecom applications
B82789*N: T
op
up to 125 °C
B82789*H: T
op
up to 150 °C
Ring core, EIA size 1812,
for automotive applications
For automotive, industrial
and telecom applications
(L
R
>4.7
mH only for tele-
com applications), reduced
height, high currents
For automotive and
industrial applications
For telecom interfaces
and ISDN systems
For telecom applications
and RF equipment
Type
V
R
V AC
L
R
mH
I
R
mA
Features
B82789C0/S0
42
B82799C0/S0
42
0.011 … 200 …
0.47
300
0.005 … 100 …
47
2000
B82793C0/S0
42
B82790C0/S0
42
0.005 … 200 …
4.7
1000
4.7 …
50
4.7 …
68
100 …
600
200 …
700
B82792C0
42
B82794C0
42
Quad chokes
B82793C2
42
0.011 … 100 …
2.2
200
0.47 …
4.7
4.7 …
10
300 …
600
200 …
300
For telecom applications
and ISDN systems
For telecom applications
and RF equipment
For telecom interfaces
and ISDN systems
B82792C2
42
B82794C2
42
Please read
Important notes
and
Cautions and warnings.
2
10/08
Data and signal line chokes
Selection guide
Leaded types
Design
Double chokes
B82796C0/S0
42
0.005 … 400 …
4.7
1200
For automotive
and telecom applications,
high currents
Type
V
R
V AC
L
R
mH
I
R
mA
Features
B82720H15
42
4.7 …
68
200 …
700
For telecom applications,
small size
B82791G15/
H15
42
2.2 …
47
100
For telecom applications,
horizontal and
vertical versions,
good RF characteristics,
without potting
Quad chokes
B82796C2
42
0.011 … 100 …
2.2
200
For telecom applications,
small size
B82720H14
42
4.7 …
10
200 …
300
For telecom applications,
compact design
B82791G14
42
0.2 … 6
100
For telecom applications,
good RF characteristics
Please read
Important notes
and
Cautions and warnings.
3
10/08
Data and signal line chokes
General
1
Data line choke applications
In the data and signal transmission it is important to ensure electromagnetic compatibility.
■
The number of systems being used for the acquisition, processing and distribution of data is con-
tinuously growing.
■
Microelectronics are spreading into new fields of application (e.g. automotive electronics).
■
The growing popularity of xDSL with its high transmission rates and worldwide networks has led
to new EMC problems.
Until recently the use of shielded cables was the main way of preventing data transmission from
being disturbed by RF interference fields. A more economical solution is the use of symmetrical
transmission line systems. In these, twisted pair lines are used in conjunction with data line chokes.
The chokes used here have extremely good symmetry characteristics.
Z
....
~
C
P
L
....
L
Z
L
Z
C
P
= Data line
choke
= Characteristic
impedance
C
P
= Parasitic
capacitances
SSB1407-X
Diagram showing the principle of a symmetrical
transmission line with data line chokes
2
Technical advantages
The main advantages are the low space requirements even for high inductance values used to
suppress common-mode interference. This is achieved by using bifilar windings, which are more
favorable for producing chokes with excellent symmetry characteristics than other winding designs.
This results in very low stray inductance, a characteristic that is highly desirable for achieving the
lowest possible attenuation of the differential-mode data signal.
Data line chokes suppress common-mode interference coupled into data lines from frequencies as
low as 1 kHz up, whereby they have no effect on data signals with bandwidths of up to several
megahertz.
Note:
To achieve the choke’s function fully, care must be taken to ensure that the vector sum of all
currents flowing through the choke is zero.
Please read
Important notes
and
Cautions and warnings.
4
10/08
Data and signal line chokes
General
3
3.1
Applications
Interference suppression on data and communication lines
Increasingly high clock frequencies/transfer rates and the associated fast rise times mean that the
signals used in modern data and telecommunications engineering are a serious potential source of
RF interference that can influence other devices and systems. At the same time, electronic data and
telecommunications equipment itself is becoming increasingly compact, which exposes it to the risk
of external conducted and radiated interference. The wide-area networking of telecommunications
equipment presents a special problem, because interference is then also able to propagate over
wide areas. To judge this, it is important to look at the different propagation modes of conducted
interference:
Differential-mode interference
(symmetrical):
The effect of differential-mode interference can be kept to a minimum by suitable, balanced design
of the transmission circuit.
One measure of this kind is the use of cables with twisted pairs. Because the conductors are routed
so close together and twisted, coupling in of differential-mode interference through electromagnetic
fields is practically impossible.
Common-mode interference
(asymmetrical):
Common-mode interference is caused by electromagnetic fields that induce interference voltages
in lines. It can only be reduced by filtering or shielding.
The most commonly used means of transmission are based on symmetrical data signals routed
over twisted pairs. Examples of this are the analog plain old telephone system (POTS) and new
digital systems like ISDN (integrated services digital network) or high-speed networks like ADSL
(asymmetrical digital subscriber line).
In all such cases, the useful signal appears as a differential-mode signal. As mentioned, the
interference coupled in by electromagnetic fields is in common mode. By appropriate protective
circuitry it is possible to suppress the interference and at the same time let the transmitted
symmetrical signal pass unaffected.
Chokes are a very effective means of protecting data lines. The different designs, optimized for
telecommunications and data applications, exhibit very low stray inductance (approx. 1‰ of rated
inductance) and excellent symmetry features. They can substantially enhance the characteristic
symmetry of a transmission line and thus contribute further to increasing interference immunity and
at the same time reducing emitted interference.
3.2
Automotive electronics
Automotive bus systems like CAN (Controller Area Network) and FlexRay
®1)
make it possible to
simplify the wiring of a vehicle considerably, enabling the same cable harnesses to be used for
vehicles fitted with different combinations of electrical equipment and appliances. In modern motor
vehicles the CAN bus has evolved as a standard. However, car electronics is a growing field. In the
past there were only a few controllers, e.g. ABS, powertrain, airbag. Nowadays, a lot of new features
for driver assistance and safety applications are already available and this is by no means the end.
1) FlexRay
®
is a registered trademark of Daimler AG
Please read
Important notes
and
Cautions and warnings.
5
10/08
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